Program crashes after sending data over libusb/Qthread for 3d time

yet another problem! i dont think this has naything to do with libusb but more with the Thread im running.

in my main thread i call a function that sets a character array in the 2nd thread (usbcom) and set a boolean to indicate there is data to send.

Code:

---

void Project::sendSettings()
{
    QString a;
    QMessageBox box;
    unsigned char *b;
    int r, transf;
    if (ui->checkBox_RPM->isChecked())
    {
        sprintf((char*)b,"*1 %d %d %d",ui->spinBox_RPM->value(), ui->spinBox_KOPPEL->value(), ui->spinBox_over->value());
        a.append((const char*)b);
        usbcom->data = b;
        usbcom->send = true;
    }
    else if (ui->checkBox_TEMP->isChecked())
    {
        sprintf((char*)b,"*0 %d %d", (char)ui->spinBox_TEMP->value(), (char)ui->spinBox_over->value());
        a.append((const char*)b);
        usbcom->data = b;
        usbcom->send = true;
    }
    else
    {
        box.setText("Must at least check one option!");
        box.exec();
    }

---

the above function is called by this SLOT:

Code:

---

void Project::button_send()
{
    if(!usbcom->isRunning())
    {
         if(checkConnection())
         {
            sendSettings();
          }
    }
    else
    {
        sendSettings();
    }
}

---

placing a breakpoint on the first line of this slot shows me that when checking "if(!usbcom->isRunning)" for the thirth time stops the program with a segmentation fault.
gdb output:

Code:

---

Program received signal SIGSEGV, Segmentation fault.
[Switching to Thread 0xb6d64700 (LWP 20232)]
0xb71bddd9 in QMutex::lock (this=0x9309cdc)
    at /var/tmp/qt-x11-src-4.5.3/src/corelib/thread/qmutex.cpp:152
152	/var/tmp/qt-x11-src-4.5.3/src/corelib/thread/qmutex.cpp: No such file or directory.
	in /var/tmp/qt-x11-src-4.5.3/src/corelib/thread/qmutex.cpp

---

what could cause this?

help is much appreciated

Sisco

So where is the thread in all this?

Quote:

---

Originally Posted by wysota

So where is the thread in all this?

---

Code:

---

void UsbCom::run()
{
    int r;
    r = libusb_init(NULL);
    send = false;
    if (r < 0)
    {
        emit error("Failed to initialize USB!");
 
    }
    devh = libusb_open_device_with_vid_pid(NULL, idVENDOR, idPRODUCT);
    if(!devh)
    {
       emit error("Could not locate device");
    }
    else
    {
        r = libusb_kernel_driver_active (devh, 0);
        if (r != 0)
        {
            if(r==1)
            {
                r = libusb_detach_kernel_driver(devh, 0);
                if (r > 0)
                {
                    emit error("some other random error:"+ QString::number(r));
                }
            }
        }
        r = libusb_claim_interface(devh, 0);
        if (r < 0)
        {
            emit error("usb_claim_interface error"+ QString::number(r));
        }
        int a = 0;
        unsigned char irqbuf[64];
        irq_transfer = libusb_alloc_transfer(0);
        libusb_fill_interrupt_transfer(irq_transfer, devh, EP_INTR_IN, irqbuf,sizeof(irqbuf), ep_irq_in_cb, &a, 0);
        r = libusb_submit_transfer(irq_transfer);
        while(1)
        {
            if(send)
            {                
                sendData();
            }
            if (a == 1)
            {                
                emit dataRecieved(irqbuf);
                a = 0;
            }
            r = libusb_handle_events(NULL);
        }        
    }    
    libusb_close(devh);
}
 
void UsbCom::sendData()
{
    int r,transf;
    QString a;
    a.append((const char*)data);
    r = libusb_interrupt_transfer(devh, EP_INTR_OUT, data, a.length(),&transf,1000);
    if (r == 0)
    {
        emit error("Configuration sent");
    }
    send = false;
}
 
void ep_irq_in_cb(libusb_transfer *transfer)
{
    if(transfer->status != LIBUSB_TRANSFER_COMPLETED)
    {
        fprintf(stderr, "uncompleted transter\n");
    }
    else
    {
        int *data = static_cast<int*>(transfer->user_data);
        *data = 1;
    }
 
    if (libusb_submit_transfer(transfer) < 0)
    {
        fprintf(stderr,"could not resubmit irq \n");
        //exit(1);
    }
}

---

sorry about that :)

How about doing proper synchronization of shared variables?

im sorry, i am still very new to this.
i have read about QMutex and QWaitCondition but i cant seem to figure out how to implement this in my code.

i tried different aproaches:

Code:

---

void UsbCom::run()
{
    int r;
    r = libusb_init(NULL);
    send = false;
    if (r < 0)
    {
        emit error("Failed to initialize USB!"); 
    }
    devh = libusb_open_device_with_vid_pid(NULL, idVENDOR, idPRODUCT);
    if(!devh)
    {
       emit error("Could not locate device");
    }
    else
    {
        r = libusb_kernel_driver_active (devh, 0);
        if (r != 0)
        {
            if(r==1)
            {
                r = libusb_detach_kernel_driver(devh, 0);
                if (r > 0)
                {
                    emit error("some other random error:"+ QString::number(r));
                }
            }
        }
        r = libusb_claim_interface(devh, 0);
        if (r < 0)
        {
            emit error("usb_claim_interface error"+ QString::number(r));
        }
        int a = 0;
        unsigned char irqbuf[64];
        irq_transfer = libusb_alloc_transfer(0);
        libusb_fill_interrupt_transfer(irq_transfer, devh, EP_INTR_IN, irqbuf,sizeof(irqbuf), ep_irq_in_cb, &a, 0);
        r = libusb_submit_transfer(irq_transfer);
        while(1)
        {
            wait.wait(mutex); //QMutex *mutex
            if(send)
            {                
                sendData();
            }
            if (a == 1)
            {                
                emit dataRecieved(irqbuf);
                a = 0;
            }
            r = libusb_handle_events(NULL);
        }        
    }    
    libusb_close(devh);
}
 
void UsbCom::sendData()
{
    int r,transf;
    QString a;
    a.append((const char*)data);
    r = libusb_interrupt_transfer(devh, EP_INTR_OUT, data, a.length(),&transf,1000);
    if (r == 0)
    {
        emit error("Configuration sent");
    }
    send = false;
}
 
void ep_irq_in_cb(libusb_transfer *transfer)
{
    if(transfer->status != LIBUSB_TRANSFER_COMPLETED)
    {
        fprintf(stderr, "uncompleted transter\n");
    }
    else
    {
        int *data = static_cast<int*>(transfer->user_data);
        *data = 1;
    }
 
    if (libusb_submit_transfer(transfer) < 0)
    {
        fprintf(stderr,"could not resubmit irq \n");
        //exit(1);
    }
}

---

Code:

---

usbcom->mutex = &mutex

---

Code:

---

void Project::sendSettings()
{
    QString a;
    QMessageBox box;
    unsigned char *b;
    int r, transf;
    if (ui->checkBox_RPM->isChecked())
    {
        sprintf((char*)b,"*1 %d %d %d",ui->spinBox_RPM->value(), ui->spinBox_KOPPEL->value(), ui->spinBox_over->value());
        a.append((const char*)b);
        usbcom->data = b;
        usbcom->send = true;
    }
    else if (ui->checkBox_TEMP->isChecked())
    {
        sprintf((char*)b,"*0 %d %d", (char)ui->spinBox_TEMP->value(), (char)ui->spinBox_over->value());
        a.append((const char*)b);
        usbcom->data = b;
        usbcom->send = true;
    }
    else
    {
        box.setText("Must at least check one option!");
        box.exec();
    }
    usbcom->wait.wakeAll();

---

this compiles fine but still gives a seg fault.
could you please explain me a little on how i should implement this?

Learn to use QMutex. There is a nice example of protecting a shared variable in its docs.

By the way, there is no reason for you to use threads here.

how would i get this so i dont need to use a thread.
right now the thread has a "while(1)" loop to check for a completed transfer.
i cant see a way to have this running without hanging the main thread.

Quote:

---

Originally Posted by sisco

how would i get this so i dont need to use a thread.
right now the thread has a "while(1)" loop to check for a completed transfer.
i cant see a way to have this running without hanging the main thread.

---

Use signals and slots (probably with a timer) instead of the while loop. There is no point in using up all your cpu resources without a reason.